I have a dog, a few months old, I just bought him yesterday. Yesterday he was playful, and he is always running and walking and following me around. Then today he was weak, he slept the whole day, he doesn't eat and I have to force him to drink water. His feces are very watery. What to do? :(

As a vet nurse, my one piece of single advice is to get him to the vets, something definitely doesn't sound right, as a puppy he needs to eat as I'm sure you know, it may be a case of nothing, but better to be safe then to be sorry
I hope he gets better soon :)